I have a javascript function which takes two arguments. First one is necessary and the second one is optional. The second argument is a callback function. How do I provide callback function as a default argument. The code that I wrote had errors. The code that I tried:
function doSomething(count,() => {}) {
//code
}
You can use default value for function parameter like below way.
function doSomething(count, fn = (() => {})) {
//code
//here fn is reference to the second parameter
}
Below is an example.
function doSomething(count,fn = (() => {})) {
console.log(fn())
}
doSomething(1, () => {return 2})you can use call methods for this scenario
function doSomeThing(param1, fn) {
// you should callback function
(fn ? fn : yourCustomeFunction).call(this)
}
Any argument not passed in to a function has the value of undefined. Just check to see if the callback is defined:
function doSomething(count,callback) {
// code
if (callback !== undefined) {
callback()
}
}
To be safer, you can also check if callback is a function:
function doSomething(count,callback) {
// code
if (typeof callback === 'function') {
callback()
}
}
function doSomething(count,callback) {
// code
if (!!callback) {
callback()
}
}
Check whether the second argument is there or not.
To provide callback as default argument, you can try :
const doSomeAction = (callback = Function()) => {
// write code here
callback();
}
doSomeAction();
However, there are lot of other ways of doing , I prefer this approach as it's cleaner.
undefined. like mentioned below.undefined.